plugins: Prefer use same format for surface and image in allocator.

We prefer to use the same format between image and surface for gst vaapi allocator. The old way may choose different formats between image and surface. For example, the RGBA image may have a NV12 surface. So we need to do format conversion when we put/get image to surface. Some drivers such as iHD can not support such conversion and always cause a data flow error. There may also have some performance cost for format conversion when put/get images. So we prefer to use the same format for image and surface in the allocator. If the surface can not support that format, we then fallback to find a best one as the surface format.